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    <script>
      let arr = [1, 2, 3]
      // 需要给默认值 
      function handleData(arr, bool = true) {
        let sum = 0
        for (i = 0; i < arr.length; i++) {
          sum += arr[i]
        }
        // bool === true在if里面冗余
        if (bool) {
          return sum
        } else {
          return sum / arr.length
        }
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      console.log(handleData(arr, true))
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